April 15 —
New research offers a
biological explanation for why toddlers are so enthralled by the game
jack-in-the-box and we all get a kick out of surprise parties. Brain scans
show humans are hard-wired to derive pleasure from such unexpected
events.

SCIENTISTS USING
magnetic resonance imaging (MRI) to measure brain activity in response to
pleasurable stimuli found that the nucleus accumbens — a region known as
the brain’s pleasure center — responded much more strongly when the event
was unanticipated. “What this means is that
the part of the brain that has always been associated with pure pleasure
really cares about when you get something unexpected,” said lead author
Dr. Gregory Berns, an assistant professor of psychiatry at Emory
University in Atlanta. “So if you get a present for your birthday, that’s
nice. But you’ll like it a lot more if you get a present and it’s not your
birthday.” Because the same region of the
brain is activated by cocaine and other drugs, the study may yield new
insights on addiction, the researchers said.

STUDY
DETAILS Twenty-five adult
volunteers underwent MRI scans while having fruit juice or water squirted
into their mouths through a tube either in a predictable or unpredictable
pattern. During the predictable run, water and juice alternated at fixed
interval of 10 seconds; during the unpredictable run, the order and
interval were randomized. The subjects were then asked which drink they
preferred. The scans revealed that the
brain’s pleasure center was most strongly activated when the squirts were
unpredictable. This held true regardless of whether the subjects preferred
juice or water.

A graphic illustrates how the
nucleus accumbens -- the area in the middle of the axis -- is activated in
response to an unpredictable event.

Activation in this area of the brain suggests a rush of dopamine —
the brain’s feel-good neurotransmitter, the researchers said.
“The region lights up like a Christmas tree on the
MRI,” said study co-author Dr. P. Read Montague, an associate professor of
neuroscience at Baylor College of Medicine in Houston. “That suggests
people are designed to crave the unexpected.”
The findings were published Sunday in the Journal of
Neuroscience. The researchers did not
examine how the brain would react to bad surprises, but Berns said that
negative stimuli are processed in a different area of the brain. He
speculated that unpredictability would probably amplify the aversiveness
of negative events just as it enhances the pleasure of pleasant
events. Berns explained the significance of
unpredictability from an evolutionary point of view: “The brain is tuned
to pick up change. It’s linked to survival. When something surprising
happens in the environment, that can be life or death.”

CLUES TO
DRUG ADDICTION

The scans also
revealed that unpredictable events activate the brain in a manner similar
to cocaine, according to Montague. This
discovery — that surprising someone with natural, healthy stimuli like
juice or water can activate the brain’s reward center to the same degree
as cocaine and other drugs — could help researchers better understand the
biological basis of drug addiction, Montague and Berns said.
“We know people take drugs because they like what it’s
doing to their brains. But what this study suggests is that what they like
is the unusual nature of the drug experience,” said Dr. Alan Leshner,
director of the National Institute on Drug Abuse, which helped fund the
research.

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Dr. George Koob, a professor of neuropharmacology at Scripps
Research Institute in La Jolla, Calif., put forth a similar
explanation. “Cocaine and other
psychostimulants make stimuli that are rewarding even more so,” he said,
“and in a sense make it like a surprise.”